1. Field of the Invention
The present invention relates to a set of a reaction liquid and an ink, and an image forming method.
2. Description of the Related Art
In the past, for the purpose of improving image performance, there has been various proposals for image forming methods that form an image by preparing, in addition to an ink containing a coloring material, a so-called reaction liquid and, for example, applying the reaction liquid onto a recording medium prior to applying the ink.
For example, Japanese Patent Application Laid-Open No. 2001-138629 proposes an image forming method in which recording is performed by causing a reaction liquid including a reaction agent that produces an aggregate when the agent comes into contact with a pigment ink, and an ink including a polymer emulsion particle having a minimum film forming temperature of 20° C. or less, to adhere to a recording medium. Further, Japanese Patent Application Laid-Open No. 2001-138629 states that examples of the reaction agent include polyvalent metal salts and a polyallylamine or a polyallylamine derivative. Japanese Patent Application Laid-Open No. 2000-263921 proposes an ink jet recording method in which recording is performed by causing an ink and a reaction liquid including a cationic water-soluble polymer to adhere to a recording medium. In addition, Japanese Patent Application Laid-Open No. 2007-84607 proposes an ink jet ink set formed from a pigment ink that contains an anionic polymer dispersant and an acidic transparent processing liquid that does not include a coloring material and that has a pH of 3.5 to 5.0. This acidic transparent processing liquid includes a pH buffering agent, which has one carboxyl group with a pKa of 3.7 to 6.5, 10 mass % or more of which is dissolved in water, and which has the property of substantially not volatilizing at 20° C. and ordinary pressure.
To provide a formed image with water resistance, scratch resistance, and highlighter resistance, typically, a water-soluble polymer is blended in the ink. Alternatively, another common method is to incorporate a water-soluble polymer in the ink by using a so-called polymer-dispersed pigment in which a water-insoluble coloring material, such as a pigment, is stabilized with a water-soluble polymer. For example, Japanese Patent Application Laid-Open No. 2004-306403 proposes an ink set that uses an ink in which a water-soluble polymer is directly bonded, or bonded via another atom group, to a pigment.
However, if a water-soluble polymer is incorporated in the ink as in the related art, for example, when plain paper and the like is used as the recording medium, although water resistance, scratch resistance, and highlighter resistance can be conferred to the image, another problem arises, in which the optical density of the image deteriorates. Therefore, the present inventors recognized that it is important to develop a reaction liquid that can be used to obtain an image having a high optical density even when various water-soluble polymers are incorporated in the ink.
Accordingly, it is an object of the present invention to provide a set of a reaction liquid and an ink that can obtain an image having high optical density while conferring water resistance, scratch resistance, and highlighter resistance to the image. Further, it is another object of the present invention to provide an image forming method which uses a set of a reaction liquid and an ink that can obtain an image having the above-described excellent properties.